U.S. patent application number 10/962982 was filed with the patent office on 2005-05-26 for high-strength steel component with zinc containing corrosion resistant layer.
This patent application is currently assigned to Benteler Automobiltechnik GmbH. Invention is credited to Danger, Elisabeth, Kroger, Matthias.
Application Number | 20050109433 10/962982 |
Document ID | / |
Family ID | 34353432 |
Filed Date | 2005-05-26 |
United States Patent
Application |
20050109433 |
Kind Code |
A1 |
Danger, Elisabeth ; et
al. |
May 26, 2005 |
High-strength steel component with zinc containing corrosion
resistant layer
Abstract
A hot-pressed and in-tool hardened structure or safety component
of a vehicle is treated with zinc dust or powder to affect zinc
diffusion into the steel surface and from a zinc/iron alloy with
corrosion resistance. The thickness of the coating is up to 10
.mu.m.
Inventors: |
Danger, Elisabeth;
(Paderborn, DE) ; Kroger, Matthias; (Brakel,
DE) |
Correspondence
Address: |
THE FIRM OF KARL F ROSS
5676 RIVERDALE AVENUE
PO BOX 900
RIVERDALE (BRONX)
NY
10471-0900
US
|
Assignee: |
Benteler Automobiltechnik
GmbH
|
Family ID: |
34353432 |
Appl. No.: |
10/962982 |
Filed: |
October 12, 2004 |
Current U.S.
Class: |
148/533 ;
428/659 |
Current CPC
Class: |
C23C 26/00 20130101;
Y10T 428/12799 20150115; C22C 38/22 20130101; C21D 1/673 20130101;
B62D 25/00 20130101; C22C 38/24 20130101; C22C 38/02 20130101; C22C
38/38 20130101; C23C 10/28 20130101 |
Class at
Publication: |
148/533 ;
428/659 |
International
Class: |
B32B 015/00; C23C
008/36 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 13, 2003 |
DE |
10348086.2 |
Claims
We claim:
1. A method of making a structural or safety component of a motor
vehicle which comprises: (a) die shaping of a blank of
high-strength steel to form said component in a press; (b)
hardening the component in said press; and (c) forming a
corrosion-resistant layer on the die-shaped press-hardened
component of step (b) by subjecting said component to a
solid-diffusion process on the surfaces of said component to
produce a zinc/iron alloy layer thereon of a thickness sufficient
to resist corrosion and .ltoreq.10 .mu.m.
2. The method defined in claim 1 wherein said layer is not
passivated.
3. The method defined in claim 1, further comprising the step of
lacquering said layer.
4. The method defined in claim 1 wherein said steel has
substantially the following composition in weight percent:
3 carbon 0.18 to 0.3% silicon 0.1 to 0.7% manganese 1.0 to 2.5%
phosphorus max. 0.025% chromium up to 0.8% molybdenum up to 0.5%
sulfur max. 0.01% titanium 0.02 to 0.05% boron 0.002 to 0.005%
aluminum 0.01 to 0.06%
balance iron and usual smelting-related impurities.
5. The method defined in claim 1 wherein said steel has
substantially the following composition in weight percent:
4 carbon 0.09 to 0.13% silicon 0.15 to 0.30% manganese 1.10 to
1.60% phosphorus max. 0.015% chromium 1.00 to 1.60% molybdenum 0.30
to 0.60% sulfur max. 0.011% vanadium 0.12 to 0.25% aluminum 0.02 to
0.05%
balance iron and usual smelting-related impurities.
6. A hot-formed, press-hardened structural or safety component of a
motor vehicle which comprises a corrosion-resistant layer on the
die-shaped press-hardened component formed by subjecting said
component to a solid-diffusion process on the surfaces of said
component to produce a zinc/iron alloy layer thereon of a thickness
sufficient to resist corrosion and .ltoreq.10 .mu.m.
7. The hot-formed, press-hardened structural or safety component of
a motor vehicle defined in claim 6 wherein said layer is not
passivated.
8. The hot-formed, press-hardened structural or safety component of
a motor vehicle defined in claim 6, further comprising a lacquer
coating on said layer.
9. The hot-formed, press-hardened structural or safety component of
a motor vehicle defined in claim 6 wherein said steel has
substantially the following composition in weight percent:
5 carbon 0.18 to 0.3% silicon 0.1 to 0.7% manganese 1.0 to 2.5%
phosphorus max. 0.025% chromium up to 0.8% molybdenum up to 0.5%
sulfur max. 0.01% titanium 0.02 to 0.05% boron 0.002 to 0.005%
aluminum 0.01 to 0.06%
balance iron and usual smelting-related impurities.
10. The hot-formed, press-hardened structural or safety component
of a motor vehicle defined in claim 6 wherein said steel has
substantially the following composition in weight percent:
6 carbon 0.09 to 0.13% silicon 0.15 to 0.30% manganese 1.10 to
1.60% phosphorus max. 0.015% chromium 1.00 to 1.60% molybdenum 0.30
to 0.60% sulfur max. 0.011% vanadium 0.12 to 0.25% aluminum 0.02 to
0.05%
balance iron and usual smelting-related impurities.
11. A method of increasing corrosion resistance of a hot-formed,
press-hardened structural or safety component of a motor vehicle,
which comprises forming a corrosion-resistant layer on the
die-shaped press-hardened component by subjecting said component to
a solid-diffusion process on the surfaces of said component to
produce a zinc/iron alloy layer thereon of a thickness sufficient
to resist corrosion and .ltoreq.10 .mu.m.
12. The method defined in claim 11 wherein said layer is not
passivated.
13. The method defined in claim 11, further comprising the step of
lacquering said layer.
14. The method defined in claim 11 wherein said steel has
substantially the following composition in weight percent:
7 carbon 0.18 to 0.3% silicon 0.1 to 0.7% manganese 1.0 to 2.5%
phosphorus max. 0.025% chromium up to 0.8% molybdenum up to 0.5%
sulfur max. 0.01% titanium 0.02 to 0.05% boron 0.002 to 0.005%
aluminum 0.01 to 0.06%
balance iron and usual smelting-related impurities.
15. The method defined in claim 11 wherein said steel has
substantially the following composition in weight percent:
8 carbon 0.09 to 0.13% silicon 0.15 to 0.30% manganese 1.10 to
1.60% phosphorus max. 0.015% chromium 1.00 to 1.60% molybdenum 0.30
to 0.60% sulfur max. 0.011% vanadium 0.12 to 0.25% aluminum 0.02 to
0.05%
balance iron and usual smelting-related impurities.
16. The method defined in claim 11 wherein said component is fixed
in a heating chamber and is coated with a sherandizing powder of
zinc on all sides at a temperature below 320.degree. C.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a method for making a
high-strength corrosion steel component as a structural member of
an automotive vehicle or as a safety-promoting member. More
particularly this invention relates to a hot-formed and press
hardened structural or safety component for a motor vehicle
composed of high-strength steel with a corrosion resistant layer
containing zinc.
BACKGROUND OF THE INVENTION
[0002] In vehicle construction, structural components and safety
components are increasingly being fabricated from high-strength
steel. In order to provide optimum strength with lightweight
constructions, high-strength steel blanks may be fabricated into
shaped structural steel and safety components for a motor vehicle
by die pressing in a hot state (hot forming) followed by press
hardening, i.e. hardening of the hot formed component in the die
(in-tool hardening). Such techniques can be used for components
like door impact beams, the A columns and B columns of an
automotive vehicle, a shock absorber longitudinal or transverse
beam (cross beam), and other structural and safety components of
the vehicle.
[0003] DE 24 52 486 C2, for example, describes a method for the
press forming and hardening of steel sheet of relatively small
material thickness to produce shaped bodies of high dimensional
stability. The steel is a boron-alloy steel and is heated to a
temperature above the A.sub.c3 temperature and shaped to the
desired final configuration in less than 5 seconds between a pair
of die members. While retaining the shaped body between these
members, the body is cooled rapidly by the indirect cooling of the
die to produce a martensitic and/or bainitic structure in the
steel.
[0004] The A.sub.c3 temperature is, of course, the temperature at
is which the ferrite to austenite transition is complete on the
heating of such a steel. Under these conditions, it is possible to
obtain a product with high shape retentivity and dimensional
stability, a precise configuration and a high-strength such that
the fabricated component is particularly suitable for use as a
structural member in a steel body of an automotive vehicle or as a
safety or crash impact absorbing component thereof.
[0005] One problem with such hot-formed, press-hardened structural
and safety components has been, however, the corrosion resistance
thereof. From DE 101 58 622 A1 it is known, for example, to apply a
layer which is strongly adherent to the steel component to serve as
a corrosion-resistant coating. The usual coating technique is a
melt immersion process, for example, a pyrogalvanisation in which
zinc is applied from a bath. Other techniques utilize galvanic
application of the zinc from an electrolyte or thermal spraying. A
cold gas coating method is also known in the art.
[0006] All of these methods have, however, various drawbacks. For
example, in a melt immersion method, large amounts of heat are
transferred from the hot bath of molten zinc into the hardened
structure of the steel component and can significantly reduce the
strength thereof. The layer thickness has limits with respect to
its minimum and the coated steel cannot be welded or can be welded
only with difficulty. Thus the melt immersion method is only a
possibility in principal and in practice cannot be used for
hot-formed hardened structural and safety components.
[0007] The spraying of the hot formed and hardened components with
zinc flakes by the so-called Deltatone process produces a coating
with limited adhesion and does not allow the coating of undercut
regions and recessed formations except with significant expense.
The coating of interior sides is practically impossible. The result
is an unsatisfactory or insufficient corrosion protection. A zinc
flake coating likewise is only limitedly weldable.
[0008] Thermal spray coatings likewise can have poor adhesion and
poor weldability. In the case of electrolytic zinc coatings, there
is the danger of hydrogen embrittlement of products with a strength
in excess of 1000 MPa. Strengths in excess of 1000 MPa are rapidly
exceeded with hot formed and hardened structural components of
high-strength steels. Electrolytic zinc coatings and cold gas
coatings are too expensive for the most part for mass
production.
[0009] EP 101 3785 describes a method in which steel strip is
produced with an aluminum immersion coating and then a blank cut
from the coated strip is heated, hot-formed and possibly treated
subsequently. The melt immersion coating forms an intermetallic
phase with the steel and the hot forming and subsequent hardening
do not detrimentally affect the coating. However, the cut edges of
the blank do not have the protective coating and if the product is
to be cold formed subsequently, the coating can be damaged. In
general, the corrosion resistance of the blank is
unsatisfactory.
OBJECTS OF THE INVENTION
[0010] It is, therefore, the principal object of the present
invention to provide a hot-formed and hardened structural or safety
component of an automotive vehicle of high-strength steel which has
a corrosion protective layer free from gaps, which suffers no
diminution in strength or only little diminution in strength as a
result of the corrosion protection in which the protective layer is
highly adherent and weldable, and can be used even in the case of
undercuts, recessed portions and internal surfaces.
[0011] Another object is to provide an improved structural or
safety component of steel for a motor vehicle which has improved
corrosion resistance.
[0012] It is also an object of the invention to provide an improved
method of making such a component and an improved method of
imparting corrosion resistance to such a component.
SUMMARY OF THE INVENTION
[0013] These objects are attained, in accordance with the invention
by providing a corrosion resistant layer in a solid state diffusion
process to produce a zinc/iron alloy with a layer thickness of at
most 10 .mu.m but of a thickness sufficient to resist corrosion.
The minimum thickness can be 0.01 .mu.m.
[0014] More particularly, a method of making a structural or safety
component of a motor vehicle comprises the steps of:
[0015] (a) die shaping of a blank of high-strength steel to form
the component in a press;
[0016] (b) hardening the component in the press; and
[0017] (c) forming a corrosion-resistant layer on the die-shaped
press-hardened component of step (b) by subjecting the component to
a solid-diffusion process on the surfaces of the component to
produce a zinc/iron alloy layer thereon of a thickness sufficient
to resist corrosion and .ltoreq.10 .mu.m.
[0018] The hot-formed press hardened structural or safety component
will thereby comprise a corrosion-resistant layer on the die-shaped
press-hardened component formed by subjecting said component to a
solid-diffusion process on the surfaces of said component to
produce a zinc/iron alloy layer thereon of a thickness sufficient
to resist corrosion and .ltoreq.10 .mu.m.
[0019] In another aspect of the invention, the method of increasing
the corrosion resistance of the hot-formed, press-hardened
structural or safety component comprises forming a
corrosion-resistant layer on the die-shaped press-hardened
component by subjecting the component to a solid-diffusion process
on the surfaces of the component to produce a zinc/iron alloy layer
thereon of a thickness sufficient to resist corrosion and
.ltoreq.10 .mu.m.
[0020] The starting point for the invention is the well known
sheradization process which in the past has been practiced with
bulk products like screws and bolts. Reference can be made in this
regard to German Industrial Standard DIN 13811 entitled zinc
diffusion coating on iron materials. Reference can also be had to
U.S. Pat. No. 6,171,359. Sheradization is a solid state diffusion
process in which the articles are brought into close contact with
zinc dust and an inert material, for example, sand and is heated to
form a zinc/iron alloy on the surface. The materials subjected to
sheradization in DIN 13811 is an unalloyed carbon steel or a low
alloy steel. The method is usually carried out in a slowly rotating
closed vessel at a temperature of 320.degree. through 500.degree.
C. The coating protects the iron articles from corrosion and wear
and in accordance with the German Industrial Standard must have a
minimum thickness of 15 .mu.m. The coating is usually subjected to
a phosphate or chromate treatment for passivation and yields a
clean passivated surface. The coating follows the contours of the
article with precision and enables uniform coating even of articles
which have an irregular shape. The sheradized coating is a
zinc/iron alloy which has high surface hardness and high wear
resistance. Scratches by contact with other articles are usually
only superficial and have not advance affect on the corrosion
resistance. The adhesion of the coating with the substrate is
strong and a characteristic of sheradization.
[0021] The good adhesion and corrosion resistance of the coating as
well as the precision with which it follows the contours of the
shaped article make the sheradization coating of considerable value
for the hot formed and hardened vehicle components of the
invention. We have found, however, in spite of teachings to the
contrary, that the normal minimum coating thickness of 15 microns
is totally unsuitable for the structural and safety components of
the invention for which a maximum coating thickness of 10 .mu.m is
essential to permit welding and for other reasons. Because the
coating is also not passivated in accordance with the invention, it
can remain conductive and can enable electronic welding techniques
is such as spot welding to be utilized. Other welding processes
like MIG or MAG welding processes can be used. The coatings can, if
required, be lacquered.
[0022] According to a feature of the invention, the article to be
coated should be rotated in a drum and it has been found to be
advantageous to anchor the article in the drum by an appropriate
framework. Otherwise, dimensional stability cannot be insured
within the necessary narrow tolerances.
[0023] Alternatively, the component to be sheradized should be
placed in a stationary heating chamber and the zinc powder or
powder mixture should be dispensed uniformly over the article, e.g.
by nozzles so that the coating is carried out from all sides. This
insures the coating of undercuts, interior walls or other surfaces
which may be difficult to coat.
[0024] The component should be sheradized so that the temperature
in the interior of the component by heat abstraction from the
coating material should not exceed 320.degree..
[0025] According to a feature of the invention, the material
treated may be a boron alloy steel which can have the composition
in weight % of
1 carbon 0.18 to 0.3% silicon 0.1 to 0.7% manganese 1.0 to 2.5%
phosphorus max. 0.025% chromium up to 0.8% molybdenum up to 0.5%
sulfur max. 0.01% titanium 0.02 to 0.05% boron 0.002 to 0.005%
aluminum 0.01 to 0.06%
[0026] balance iron and usual smelting-related impurities.
[0027] After hot forming and hardening, this steel has an elastic
limit R.sub.p0.2 which is .gtoreq.950 MPa, a tensile strength
R.sub.m and an elongation A5.gtoreq.8%.
[0028] At 320.degree., the formation of the corrosion resistant
coating can be effected without substantial adverse effect on the
strength. The following steel composition in weight % can also be
used:
2 carbon 0.09 to 0.13% silicon 0.15 0.30% manganese 1.10 1.60%
phosphorus max. 0.015% chromium 1.00 to 1.60% molybdenum 0.30 to
0.60% sulfur max. 0.011% vanadium 0.12 to 0.25% aluminum 0.02 to
0.05%
[0029] balance iron and usual smelting-related impurities.
[0030] This steel has a tensile strength R.sub.m.gtoreq.950 MPa, a
yield point R.sub.p02 of .gtoreq.700 MPa and an elongation A5 of
.gtoreq.14% in an air hardened state. This type of steel also
hardens in air. However, to avoid varying the strength
characteristic, the coating process is carried out at a temperature
of 320.degree. C. in zinc dust and sand.
[0031] The structural or safety component of the invention which
results from this method has a high shape precision and good
material properties like high-strength and ductility. With the
system of the invention, it also has an extraordinary corrosion
resistance by comparison with other techniques since the diffused
layer has excellent adhesion, high wear resistance and hardness.
The coating can be found to be effective on undercuts and interior
surfaces as well as upon the edges of the workpiece. The workpiece
can be easily welded and lacquered.
BRIEF DESCRIPTION OF THE DRAWING
[0032] The above and other objects, features, and advantages will
become more readily apparent from the following description,
reference being made to the accompanying drawing in which:
[0033] FIG. 1 is an elevational view of a B column of a vehicle to
which the invention is applicable;
[0034] FIG. 2 is a perspective view in highly diagrammatic form and
partly broken away showing the corrosion treatment of the B column
of FIG. 1; and
[0035] FIG. 3 is a block diagram illustrating the method of the
invention.
SPECIFIC DESCRIPTION
[0036] FIG. 1 shows a B column of a passenger vehicle with complex
geometry. The B column serves as a structure and safety component
between the front door of a vehicle and the rear passenger
compartment.
[0037] The B column 1 must, in the case of side impact or a crash
of some other type, guarantee the stability of the passenger
compartment and thus take up significant force, resist rupture and
yield to absorb the impact. It is as a result, fabricated from a
hardenable steel and especially a sheet steel. In order to import
the desired configuration with precision and to insure that the
material will have the desired characteristics, it is heat formed
in a press between dies in the hot-forming step 10 of FIG. 3 and
while in the die is hardened at 11. The in-tool hardening is
effected by passing a liquid coolant through the dies.
Alternatively, it can be cold formed in a number of steps and only
in the last step heated to a temperature above the A.sub.c3
temperature and pressed to its final shape in the hot-forming die,
where upon the hardening is carried out in the die as has been
described. After hardening, the workpiece is subjected to
sheradizing coating in step 12 (FIG. 3) at say 320.degree. C. For
this purpose, the workpiece 1 is mounted in a framework 13 of a
slowly rotatable drum 14 driven by a motor 15 and contacted with a
zinc/sand powder mixture 16 while heated to the sheradizing
temperature utilizing the heaters represented diagrammatically at
17 and 18. The coating is formed to a thickness of say 5 .mu.m and
consists of a zinc-iron alloy formed by the diffusion of zinc into
the steel surface.
* * * * *